why does the E-M1's video get dissed?

As lab D says, the biggest complaint is lack of 24p. At 30p, I doubt most could tell the difference between cameras. I doubt I could. Panasonic probably has a better CODEC, the software the camera uses to compress the image (some are better than others). Because Panasonic makes a lot of professional video equipment I believe that knowledge carries over into their consumer line, where they don't have a strong "stills" camera edge. Panasonic cameras also have a lot of configuration choices geared to the videographer. Interestingly, only Olympus has in-camera stabilization for video at the moment. That's not to be sneezed at In fact, some would rather have that than 24p.